Soil Stratigraphy Delineation by VisCPT

The traditional CPT and CPTU tests are very good tools for stratigraphic soil logging. Using empirical techniques based on tip resistance, local friction and excess pore pressure, a continuous soil profile can be established which is more detailed than that obtained by a conventional SPT test and sampling. However, because tip resistances are controlled by the mechanical soil properties averaged over at least 5–10 cone diameters of elevation, and because the local friction is measured over a 13 cm distance, even the CPT cannot easily discern relatively thin lenses and seams in the stratigraphy. Such lenses may nevertheless control the hydrologic and mechanical behavior of a site. The vision cone penetrometer (VisCPT) collects a continuous stream of magnified images of the soil stratigraphy and thus, every lens and seam is identified. The present paper demonstrates that textural image indices show very high correlation to soil stratigraphy, as confirmed by high quality continuous borehole samples, while the CPT alone often misses or misinterprets the constituents of thin lenses and seams.